The acetal compound is the reaction product of an alditol and benzaldehyde. Alditol acetals, such as 1,3:2,4-bis(4-methylbenzylidene) sorbitol (MDBS) and 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) derivative compounds are known compounds which find their utility as an additive in polypropylene. Acetals of substituted and unsubstituted aldehydes are also known to be useful as nucleating agents, gelling agents, processing aids, and strength modifiers in polyolefin resins, polyester resins, deodorant, and antiperspirant compositions; hydrocarbon fuels and paints.
Acetal alditols are typically prepared by the condensation reaction of an aromatic aldehyde with an alditol containing 6 carbon atoms like sorbitol. For MDBS and DMDBS structures, such reactions involve two moles of the aldehyde and one mole of an alditol.
Several methods for the preparation of acetal-alditols have been reported in U.S. Pat. No. 4,267,110, U.S. Pat. No. 3,721,682, U.S. Pat. No. 4,429,140; U.S. Pat. No. 4,562,265; U.S. Pat. No. 4,902,807; U.S. Pat. No. 5,023,354; U.S. Pat. No. 5,731,474 and U.S. Pat. No. 6,500,964.
The hitherto reported methods suffer from several shortcomings. Majority of the earlier known processes employ various organic solvents which necessitates high temperature for carrying out the reaction thereby increasing the cost component. Furthermore, most of solvents are very expensive and they too render the process un-economical.
Attempts have been made in the past to overcome the above mentioned shortcomings by employing the acidic catalyst for improving the yield and the versatility (ability to employs variety of substituted aldehydes) the process.
The presently known processes for the preparation of acetals which employ acidic catalysts still suffer from several limitations. Though mineral acids serve as good catalysts for the acetalization process, they are very corrosive in nature. Furthermore, the final product resulting from such processes needs to be purified by neutralizing the residual free acid. Though the yields offered by all teachings are acceptable for the practical purposes, all the methods are not effective from the perspective of versatility, environmentally friendliness, energy efficient, reliability, cost-effective, and safe production.
Ionic systems, which are examples of viscous molten salts, have a number of interesting and useful properties, and have utility, for example, as highly polar solvents, co-solvents and catalyst in synthetic chemistry. They also have been found to be useful in applications in various fields such as electrochemistry, synthesis of chemical compounds, dyes, batteries, fuel cells, photovoltaic devices, electro-deposition processes, semi conductor cleaning, pyrolysis, gasification, in applications involving cellulose dissolution, for the electroplating of metals as described, for example in U.S. Pat. No. 6,573,405, U.S. Pat. No. 7,183,433, U.S. Pat. No. 7,196,221, US Patent Appl. No. 2005/0147889, U.S. Pat. No. 6,527,977, US Patent Appl. No. 2008/0307703, US Patent Appl. No. 2006/0183654, US Patent Appl. No. 2009/0247432.
Ionic compounds/liquids exhibit very low or no vapour pressure and thus, in contrast to many conventional molecular solvents produce virtually no vapours. They are therefore advantageous from a health, safety and environmental point of view.
Processes for preparation of acetals and di-acetals other than MDBS and DMDBS structures using ionic liquids as catalysts and/or reaction medium have been reported. For example, CN 101440025 discloses a method for preparation of ethylidene ether or ketal which employs N-methyl glyoxaline bisulphate ionic liquid catalyst. Other patents which disclose the use of ionic liquid as catalyst for preparation of acetals other than MDBS and DMDBS structures include CN 101723852, CN 101544628 and CN 1858048.
None of the hitherto reported processes for preparation of MDBS and DMDBS have employed ionic compounds/liquids as catalysts and/or reaction medium. There exists a need for process for preparation of MDBS and DMDBS which uses ionic compounds/liquids as the catalyst and or reaction medium. There also remains a need for a process for preparation of acetals, particularly MDBS and DMDBS which does not employ any expensive solvents and corrosive mineral acids.